The present disclosure relates generally to a tube hydroforming process.
Hydroforming is a cost-effective way of shaping malleable metals into lightweight, structurally stiff and strong pieces. Non-limiting examples of malleable metals include aluminum or steel. One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes possible by hydroforming to produce stronger, lighter, and more rigid unibody structures for vehicles. This technique is also particularly popular with the high-end sports car industry, and is also frequently employed in the shaping of tubes for bicycle frames.
The tubular hydroforming process involves the application of fluid pressure to the inside of a tubular blank, which is captured within a mold cavity that defines the shape of the finished part. The internal fluid pressure is then increased to force the tubular blank to expand into conformance with the mold cavity, thus taking the shape of the finished part.
Accordingly, hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to press working material into a die. To hydroform material into a vehicle's frame rail, a hollow tube is placed inside a negative mold that has the shape of the desired end part. High pressure hydraulic pistons may then inject a fluid at very high pressure inside the material which causes it to expand until it matches the mold. The hydroformed member is then removed from the mold.
Hydroforming allows complex shapes with concavities to be formed, which would be difficult to manufacture with standard solid die stamping. Furthermore, hydroformed parts can often be made with a higher stiffness-to-weight ratio and at a lower per unit cost than traditional stamped or stamped and welded parts.
In a traditional hydroforming process, a male die and a blank holder is generally used. There is generally no need to fit a female die to the punch, which means that more complex shapes can be easily formed. The single die setup also improves the speed at which die changes can be made. Since the pressure is adjusted on a continuous basis, parts which might take two or three conventional deep draws can be done in one hydroforming operation.
A flexible diaphragm helps eliminate the marks that are usually formed in deep drawing operations. This reduces costs that are related to the finishing of the final part. Due to the fact that the metal is not bent or stretched but formed around the punch, the material thin-out in the walls of the part is usually less than 10%. Thus, thinner blanks can be used to form the parts desired. This is advantageous, e.g., when using expensive materials or when the weight of a component must be carefully controlled, as in the aerospace or automotive industry. At the same time, the material is not work-hardened in a hydroforming process as it would be for a normal drawing process, so the end part usually does not have to be annealed.
Since it is not necessary to form the punch from hardened steel, cast iron is usually used to make the punch and blank holder. This material is easily machinable and has a long lifespan.
Some of the difficulties surrounding hydroforming processes are the pressures involved in forming the piece. Because the pressures involved are usually three to four times those normally associated with deep drawing, attention is generally paid to the pressure vessel to prevent fluid leaks. If too little pressure is applied, the blank may wrinkle, resulting in poor quality. If too much pressure is applied, the blank may sheer, and the part will have to be scrapped.